When it is desired to operate imaging devices such as cameras or infra-red imaging systems on moving vehicles such as aircraft, automobiles or boats, it is usually necessary for the imaging device itself to be stabilized in some manner. For example, U.S. Pat No. 3,638,502 (Leavitt et al) issued Feb. 1972 describes a stabilized camera mount in which the camera is supported from a universal joint centrally located in a spherical protective fairing, the universal joint in turn being supported by a compliant vibration isolator. A set of three orthogonal gyroscopes is attached to the camera platform, and the reaction forces from the gyroscopes tend to stabilize the platform directly. Additionally, angle transducers on the precession axes of the gyroscopes are used to sense angular rates and to automatically apply correcting moments to the platform using a combination of moving weight servos and magnetic torque motors as in the above-mentioned patent, or by means of three magnetic torque motors driving the three axes of the universal joint as in U.S. Pat. No. 4,989,466 (Goodman) issued Feb. 5, 1991. In each case, the various axes of the universal joint are used to constrain motion, so that conventional magnetic torque motors can be used. These must be mounted on the structures of the universal joint and occupy a substantial volume at the centre of the assembly which could be better used to house the payload, i.e. the imaging device.
In such prior art, the structure of the stabilized platform must be relieved in areas where it can otherwise interfere with the structure supporting the compliant vibration isolator and universal joint, thus resulting in loss of further possible payload space. Even with this loss of space, the manoeuvrability of the supporting vehicle is invariably restricted when carrying such prior art assembly.
Another problem arises with such prior art. If it is necessary, for example with an aircraft installation, to fly over an object on the ground and at the same time to track the object with a camera, the elevation over azimuth steering geometry of such prior art may prevent the operator from achieving this due to a phenomenon known as gimbal lock.